the term "go between" or "go-between" refers to a person who is utilized by two or more people as a messenger or conduit of information despite the fact that the information does not pertain to him or her.

Go Between: Yo bitch-ass friend keeps using me as a go-between, can I get paid for dat?

Asshole: Can you tell my friend I said to kiss my ass for me, dogg?
Go Between: Hell naw!!
Asshole: You fired.
Go Between: I never got paid.